GaN Substrate Melt Back for Crack-Free Growth
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Solution Overview
Problem
Existing methods for producing Group III nitride semiconductor substrates using the Na flux method are cumbersome and prone to cracking, especially when growing thick layers, due to differences in linear expansion coefficients and lattice constants between sapphire and GaN.
Innovation Solution
A method involving a template substrate with a sapphire substrate and a first Group III nitride semiconductor layer, where the layer is melted back to expose the sapphire, and a second layer is grown without filling the gaps, allowing for controlled crystal growth conditions to prevent cracking during separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a template substrate with a continuous GaN layer is used and GaN is grown to fill all spaces, then a complete thick GaN layer is produced, but stress-induced cracking occurs due to difference in linear expansion coefficient between sapphire and GaN
Solution Approach 1:
The GaN layer is segmented into isolated islands rather than forming a continuous layer. By controlling crystal growth conditions so that GaN crystals grow only on the template substrate and not on the sapphire surface, the layer is divided into discrete segments that are spaced apart, preventing stress-induced cracking while maintaining structural integrity
Solution Approach 2:
Different regions of the substrate surface are treated differently: the template substrate regions promote GaN crystal growth while the sapphire regions do not. This creates local variations in material properties and growth behavior, allowing GaN islands to form only where desired and preventing stress accumulation across the entire substrate
2Ease of manufacture
If dry-etching is used to form stripe-pattern GaN layer, then a template for flux method is created, but the production process becomes very cumbersome
Solution Approach 1:
The template formation and crystal growth steps are merged into a single flux method process. By directly growing the GaN layer on the template substrate using molten salt flux, the need for separate dry-etching steps is eliminated, simplifying the overall production process while achieving the desired stripe-pattern structure
Solution Approach 2:
The production process utilizes changes in physical parameters (temperature, pressure, flux composition) to control crystal growth directly on the template substrate. By adjusting these parameters, the GaN layer forms with the desired pattern without requiring mechanical or chemical etching steps, reducing process complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables the production of high-quality, crack-free Group III nitride semiconductor substrates, particularly effective for thick layers, by streamlining the production process and preventing stress-induced cracking.
Implementation Method 1
melt back a part of the first Group III nitride semiconductor layer to such a depth that the sapphire substrate is exposed
Implementation Method 2
a second Group III nitride semiconductor layer having a c-plane as a main plane is grown on the first Group III nitride semiconductor layer under the conditions where crystal growth of the Group III nitride semiconductor is permitted
Implementation Method 3
cooling the stacked product, to thereby generate stress attributable to the difference in linear expansion coefficient between sapphire and GaN and separate the seed crystal
Data Source
AI summary
A method for producing a Group III nitride semiconductor includes reacting a molten mixture containing at least a Group III element and an alkali metal with a gas containing at least nitrogen, to thereby grow a Group III nitride semiconductor crystal on the seed crystal. The method includes forming a template substrate including a sapphire substrate and a first Group III nitride semiconductor layer as the seed crystal which is formed by vapor phase growth and which includes a c-plane as a main plane is employed, and the template substrate is placed and maintained in the molten mixture under conditions where crystal growth of the Group III nitride semiconductor is inhibited, to thereby partially melt back a plurality of separated parts of the first Group III nitride semiconductor layer to such a depth that the sapphire substrate is partially exposed.